In the canning industry, the liquid level in cans is periodically checked in production to insure that the cans are filled to the desired level with the food product. In addition, quality control personnel will occasionally remove groups of cans from the production line to check various properties of the food product, as well as checking the liquid level in the can.
In the past, a precision metal gauge has been used to check the liquid level in the cans, and the conventional gauge has been fabricated from an elongated bar having a series of probes or fingers of graduated length. The gauge is placed on the top edge of the can and the operator visually determines, by looking into the can, which of the probes is at the liquid level, thus determining the headspace in the can.
The use of the metal gauge, as used in the past, has serious drawbacks in that it is difficult to visually determine which of the probes was in contact with the liquid level. Furthermore, the gauges as used in the past were relatively expensive instruments in that it was necessary to fabricate the gauge from corrosion resistant metal and the probes had to be precisely machined.